Migratory Songbirds & Grazing

Livestock grazing is pervasive and managed by private landowners, federal agencies, and state agencies across the west, and wildlife conservation objectives are often primary considerations in grazing management programs. Most recently, the Natural Resources Conservation Service (NRCS) has embarked on the Sage-Grouse Initiative (SGI), which provides for grazing management on private lands over a vast area with the intent of benefitting sage-grouse. Sagebrush-obligate migratory birds respond quickly to habitat changes by shifting their distributions and adapting their reproductive performance. Thus these birds can serve as an initial barometer of sagebrush ecosystem integrity and the impacts of grazing management designed to positively benefit avian communities. In 2012, we initiated a research project building off of the existing infrastructure established by Montana Fish, Wildlife, and Park’s (MTFWP) sage grouse research, to evaluate the impact of SGI’s rest-rotational grazing regimes on migratory bird species associated with sagebrush landscapes. The results of this study will inform sustainable and economically viable land management practices that maintain habitat for migratory birds.

Concomitant with a decline in sagebrush systems is a decline in grassland-, shrub-, and sagebrush-associated birds. Approximately 76% of birds that are sagebrush, desert, or chaparral obligates are declining nationally (North American Bird Conservation Initiative 2009). Shrub-nesting species make up the largest number of Species of Continental Importance within the Intermountain West (Rich et al. 2004). The greater sage-grouse, a candidate species under the Endangered Species Act, has shown significant declines over the last 30-40 years (Graton et al. 2010). Several other birds found in Montana’s sagebrush and shrub-grass systems are of conservation concern because of declining population and high threats, including Brewer’s sparrow, sage thrasher, loggerhead shrike, and lark bunting (Casey 2000, Rich et al. 2004). Grasshopper sparrows are also of conservation concern and may be found in the grassland associated with shrub-steppe systems (Knick et al. 2003, Rich et al. 2004). Therefore, conservation actions directed at sagebrush ecosystems or sage-grouse habitats in particular may provide substantial conservation benefits for other birds (Rich et al. 2005).

Livestock grazing is the most widespread land use across the range of sagebrush ecosystems (Knick et al. 2010), so effects of livestock grazing on sagebrush ecosystems and the associated bird populations are likely to be widespread. Management of livestock grazing therefore theoretically could be manipulated to positively affect populations of sagebrush-associated birds. Depending on the timing and utilization rates of livestock, livestock grazing can directly increase sagebrush size, cover, and density, decrease forb cover and density, and decrease grass cover and density (Beck and Mitchell 2000, Crawford et al. 2004). Heavy livestock grazing can also decrease invertebrate biomass (Krausman et al. 2009), which is important because invertebrates area a food source for several bird species. Rest-rotation grazing strategies area a common tool used to improve habitat for wildlife in managed sagebrush ecosystems. For example, MTFWP currently funds approximately 600,000 acres of rest-rotation grazing systems in Montana. More recently, due to emphasis on conservation for the greater sage-grouse the NRCS has developed the SGI. In Montana, delivery of this initiative includes implementation of rest-rotation management to control the location and timing of grazing on areas with relatively high sage-grouse densities, called “core” areas. To date, 120,000 acres have been enrolled, and this program is likely to grow substantially.

Despite the ubiquitous distribution of livestock grazing in sagebrush ecosystems and the widespread and growing use of rest-rotation grazing management to benefit wildlife in these areas, little data exist to demonstrate an empirical link between livestock grazing, sage-grouse habitat, and sage-grouse populations (Krausman et al. 2009). For example, an empirical link between livestock grazing, sage-grouse habitat, and sage-grouse populations has not been established (Connelly and Braun 1997, Beck and Mitchell 2000, Connelly et al. 2004, Knick et al. 2010). Limited data suggest that rest-rotation grazing may not have large short-term effects on the density of songbirds (Lapointe et al. 2003). A clear need exists to evaluate the relationship between rest-rotation livestock grazing management and sagebrush-, shrub-, and grassland-associated bird populations.

Catherine Wightman

Justin Gude

Financial support for this project has been provided by Pittman-Robertson funds issued to Montana Fish, Wildlife, and Parks (FWP) by the U.S. Fish and Wildlife Service (USFWS), the US Geological Survey Montana Cooperative Wildlife Research Unit, FWP Nongame Checkoff dollars, State Wildlife Grants issued to FWP, Plains and Prairie Pothole Landscape Conservation Cooperative (USFWS), Bureau of Land Management, OnXmaps, and the University of Montana.